Master Builders revisited: The importance of feedback loops: a case study using salvaged timber and wooden nails only

In the light of today’s challenges regarding sustainable solutions for the built environment, our research focuses on building entire structures with timber only. Salvaged timber and wooden nails are selected as starting points to explore the structural and architectural possibility by following a timber-only concept. Reminding of the ancient Master Builder idea, the process of our investigations makes clear the importance of all steps and their distinct insights feeding back, following the loops from design to the assembly of the objects, in order to increase the efficiency of material use and optimize the functionality of the final object. In this paper we evaluate the feedback loops performed so far including the lessons learnt from success and failure in design, testing and manufacturing. We also look into the potential of increased structural and architectural quality of outputs and increased diversity of applications by our approach.Peer reviewe

Graphic statics: projective funicular polygon

Since its birth, around the mid-19th century, graphic statics has been through several stages, with the most recent one being its “renaissance” phase, due to mainly the development of digital graphical tools, after almost being abandoned during the last two thirds of the 20th century. The power of graphic statics rises from the reciprocity between its two main pillars, namely the force polygon and the funicular polygon. These two pillars, tend to represent in the modern era two distinct disciplines: architectural (form) and structural engineering (force). To this end, graphic statics can act as the common ground, as we move, potentially, towards the direction of the multidisciplinary master-builder approach. The majority of graphic statics applications, in its “renaissance” phase, reported in the literature is related to form-finding of axially-loaded statically determinate structures. In the current work, we suggest a so-called projective funicular polygon, that is necessary for the structural analysis of statically indeterminate beams with inclined loads that impose an axial force component to the beam. In addition, the construction of the projective funicular polygon explicitly defines the bending moments, shear forces and axial forces in the beam and therefore provides information regarding an efficient cross-sectional variation of the beam element, while the classical funicular polygon provides information regarding an efficient alternative structural form. Finally, apart from highlighting that graphic statics is a powerful tool not only for form-finding, but for structural analysis as well, it is worth emphasizing that the information provided by the polygons (force, funicular, projective) can help us generate insights in the light of geometry towards more efficient and sustainable structures.Peer reviewe

An integrated architectural and structural design concept by using local, salvaged timber

Our research-based design approach suggests an integrated architectural and structural design concept by using local, salvaged timber in a “material and connection – structure – architecture” sequence, which is in line with Neri Oxman´s discussion of the “Form First, Structure First, Material First: the Designer’s Causality Dilemma”. Following the philosophy of design-build, locally available, salvaged wooden material connected by wooden nails only is the main design driver. The material, its properties, size, and availability as well as the wooden nail connection are explored separately. The merger of material and the specific connection results in structurally tested prototype-assemblies and in previously unnoticed insights respectively. Together with long-term observation from exposure to the natural environment as well as architectural requirements according to its prototypical use, the findings from the prototype-assemblies are feeding back the design process, as finally showcased by a natural trail project for the city of Kouvola, Finland. The proposed trail meets the requirements of a cheap, fast, replaceable, and sustainable solution, by simultaneously including multiple modular elements for the path and a central, partly curved plaza-like area. Future work will focus on smoothening the workflow and on structural and architectural optimization with special focus on the wooden nail connections, and associated assembly geometries.Peer reviewe

Sustainable design concepts for short span, timber-only structures

The construction sector is one of the major contributors to greenhouse gas emission. Therefore, sus- tainability and more environmentally friendly structural concepts and structures structures are becoming increasingly relevant. Timber, as a natural grown building material, can play a key role in this process, in particular due to its large potential of reducing CO2 emissions. Currently, salvaged material from the fabrication process of engineered wood products or from construction processes is incinerated for energy recovery. Thus, the full environmental potential of timber has not yet been achieved. In this study, a novel, low-tech design concept for short span structures is introduced. The structural system is entirely based on wooden products, including salvaged material. Individual timber boards with uniform or variable dimensions are connected with hardwood nails to load bearing members. At present, the used hardwood nails contain a minimum amount of adhesive, which is attributed to the production process, but in the long run, the project is aiming for timber-only structures. This paper presents a range of design proposals for different batches of salvaged materials having differ- ent dimensions. Our approach is driven by the following three guiding aspects: firstly by the limitation of the possible timber board patterns, which result from the used material; secondly by the assembly process, which aims for the ease of use and its robustness against assembly-errors; thirdly by the arrangement of the nails, which allow for the highest possible grade of flexibility in design and material use and which respect the aforementioned aspects. Experimental investigations of the connection between adjacent timber boards using hardwood nails have been performed. Due to the variable dimensions of salvaged material a wide range of hardwood nails and different nails patterns have been investigated. Based on the results of the experimental investigations, the main findings, which are relevant for the above mentioned guiding aspects, are summarized and discussed. The application of the design concept is exemplified in a natural trail path containing short span bridges in the Kouvola region in southern Finland.Peer reviewe

Shear capacity of timber-to-timber connections using wooden nails

With increasing environmental concerns, the building sector must rethink the selection of building materials not only for structural members but also for connections. Densified wooden nails might become an alternative to metallic fasteners, at least in applications with lower structural requirements. However, their structural behaviour in timber-to-timber connections is not yet systematically studied. This paper presents a series of 90 shear tests to explore the shear capacity and slip modulus of timber-to-timber connections with wooden nails. Specimens with different nail dimensions, different nail orientations, and different nail arrangements were investigated. A typical three-member push-out test setup was adopted where the wooden nails were oriented perpendicular or inclined to the shear plane. Specimens with inclined nails exposed to shear and tensile forces showed a higher shear resistance due to the activated tensile capacity of the wooden nails. Failure of the wooden nails was predominantly observed when the nails were loaded in tension. This means that the interface between the wooden nails and the timber did not fail. Based on the results from the shear tests, an analytical model was developed to predict the load bearing capacity of timber-to-timber connections exposed to bending stresses. The analytical model was validated with experimental investigations.Peer reviewe